Synergistic Effect of V/S Co-Doping on Boosting the Conductivity and Stability of LiMn _0.6 Fe _0.4 PO ₄ Cathodes for Lithium-Ion Batteries

Lithium manganese iron phosphate (LMFP) is considered a promising cathode material for next-generation lithium-ion batteries due to its high operating voltage and enhanced energy density compared to lithium iron phosphate (LFP). However, its commercial viability is hindered by poor intrinsic electronic conductivity and rapid capacity fade caused by Jahn–Teller distortion. Herein, we propose a strategy of vanadium and sulfur co-doping to fabricate a carbon-coated LiMn0.6Fe0.4PO4 cathode material (VS-LMFP) via a scalable solid-state synthesis. Rietveld refinement of X-ray diffraction patterns and advanced microscopy techniques confirm that V and S are successfully incorporated into the crystal lattice without forming secondary phases, inducing subtle structural modifications. Density functional theory calculations reveal that this co-doping reduces the band gap from 0.51 to 0.4 eV, significantly enhancing the intrinsic electronic conductivity. The resulting VS-LMFP cathode exhibits an excellent initial discharge capacity of 156.7 mAh g−1 at 0.1 C and maintains 125 mAh g−1 after 600 cycles at 1 C, demonstrating superior rate capability and cycling stability. The enhanced performance is attributed to the synergistic effect of V and S co-doping, which improves Li+ diffusion kinetics, stabilizes the structure against Jahn–Teller distortion, and reduces charge transfer resistance. This work provides a fundamental insight into the mechanism of co-doping and offers an effective pathway for the rational design of high-energy-density, durable cathode materials.